High Energy Physics - Phenomenology

Title:
The branching ratio $ω\to π^+π^-$ revisited

Abstract: We analyze the most recent data for the pion vector form factor in the
timelike region, employing a model-independent approach based on dispersion
theory. We confirm earlier observations about the inconsistency of different
modern high-precision data sets. Excluding the BaBar data, we find an updated
value for the isospin-violating branching ratio $\mathcal{B}(\omega \to
\pi^+\pi^-) = (1.46\pm 0.08) \times 10^{-2}$. As a side result, we also extract
an improved value for the pion vector or charge radius, $\sqrt{\langle
r_V^2\rangle} = 0.6603(5)(4)\text{fm}$, where the first uncertainty is
statistical as derived from the fit, while the second estimates the possible
size of nonuniversal radiative corrections. In addition, we demonstrate that
modern high-quality data for the decay $\eta' \to \pi^+\pi^-\gamma$ will allow
for an even improved determination of the transition strength
$\omega\to\pi^+\pi^-$.